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People blinded by light could
be treated with more light. Researchers have found that shining near-infrared
radiation on damaged retinal cells can keep them alive and prevent permanent
blindness.
The US Defense Advance Research Projects Agency (DARPA) is funding research
into the method and hopes to use it to treat people whose eyes are damaged
by lasers. A number of US military personnel, including a helicopter pilot
over Bosnia in 1998, have suffered laser eye injuries.
If the infrared technique works
in people, it could be used to treat a wide range of eye injuries and
diseases. And it does not stop there.
Other studies have shown that
infrared light can help heal all sorts of injuries and sores, and it is
already being used to treat severe mouth ulcers in children undergoing
chemotherapy.
Cell
Powerhouses
In the late 1990s, lab studies
on cells showed that near-infrared wavelengths can boost the activity
of mitochondria, the crucial powerhouses in cells. That caught the attention
of NASA, which hoped it could use the technique to treat astronauts in
space, where injuries heal more slowly than on Earth, possibly because
mitochondria do not function properly.
The treatment requires high-intensity
light, but instead of lasers, NASA has developed powerful light-emitting
diodes for the job. Lasers tend to damage cells, whereas LEDs can deliver
light in a way that is less harmful to tissue (New Scientist magazine,
25 September 1999, p 20). Now Harry Whelan, a neurologist at the Medical
College of Wisconsin in Milwaukee, and his colleagues have put the LEDs
to the test on eye injuries.
In a study that will appear
in Proceedings of the National Academy of Sciences, Whelan blinded rats
by giving them high doses of methanol, or wood alcohol. This is converted
by the body into formic acid, a toxic chemical that inhibits the activity
of mitochondria. Within hours, the rats' energy-hungry retinal cells and
optic nerves began to die, and the animals went completely blind within
one to two days.
But if the rats were treated
with LED light with a wavelength of 670 nanometres for 105 seconds at
5, 25 and 50 hours after being dosed with methanol, they recovered 95
per cent of their sight. Remarkably, the retinas of these rats looked
indistinguishable from those of normal rats. "There was some tissue
regeneration, and neurons, axons and dendrites may also be reconnecting,"
says Whelan.
Painful
Sores
The results have raised the
hope that the LED technique could be used to treat people for a range
of eye diseases known to be caused by mitochondrial problems. Whelan also
thinks it will help treat laser injuries to the retina, apart from areas
where cells have been completely destroyed.
Whelan has already tested the
LEDs on 30 children suffering from mucositis, a painful side effect of
cancer chemotherapy. The children had painful sores in their mouths and
throats and were unable to eat or drink, he says.
The LED treatment eliminated
the mucositis and is now being used to prevent it. "It's a night
and day difference in the children's floor," he says. The results
appeared in the Journal of Clinical Laser Medicine and Surgery in December
last year. The Food and Drug Administration has now approved further trials
in hospitals, which will use LEDs donated by NASA.
What is not yet clear is exactly
how the light stimulates healing. But Britton Chance of the University
of Pennsylvania has shown that about 50 per cent of the near-infrared
light is absorbed by mitochondrial proteins called chromophores. Whelan
and his colleagues think the light boosts the activity of a chromophore
called cytochrome c oxidase, a key component of the energy-generating
machinery.
New
Scientist July 12, 2002
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